This invention relates generally to an apparatus and method for measuring neutron energy and more particularly, but not by way of limitation, to a neutron detector and method utilizing a lithium tantalate crystal disposed in an oil or gas well.
There are many areas in which neutrons need to be detected and their energy measured. Neutrons are used in logging oil and gas wells. Medical equipment uses neutrons which need to be sensed for providing diagnostic/therapeutical information. Nuclear reactors use and produce neutrons whose energy needs to be monitored. Neutrons are also monitored in outer space projects.
In well logging, for example, neutrons can be detected by presently known devices. These typically include a medium which undergoes nuclear reactions in response to neutrons entering the medium and striking nuclei in the medium. Lithium fluoride and gaseous helium-3 are examples of media which have been used in neutron detectors used in the oil and gas industry. Charged pairs of alpha particles (helium-4 atoms) and/or hydrogen atoms (hydrogen-1 and/or hydrogen-3) are generated in these media in response to neutrons striking the nuclei of the lithium or helium atoms. Upon passing into another medium outside the generating medium, these charged pairs are sensed and signals generated representing the energy of the impinging neutrons.
A shortcoming of the foregoing technique is that energy loss occurs when the charged pairs pass from one medium to another for detection. Lower energy resolution results. There is the need for an improved detecting technique which avoids this loss of resolution.